September 13, 2012

Study Of Giant Viruses Shakes Up Tree Of Life

by editor

A new study of giant viruses supports the idea that viruses are ancient living organisms and not inanimate molecular remnants run amok, as some scientists have argued. The study reshapes the universal family tree, adding a fourth major branch to the three that most scientists agree represent the fundamental domains of life.

"The giant viruses have incredible machinery that seems to be very similar to the machinery that you have in a cell," he said. "They have complexity and we have to explain why."

Part of that complexity includes enzymes involved in translating the genetic code into proteins, he said. Scientists were startled to find these enzymes in viruses, since viruses lack all other known protein-building machinery and must commandeer host proteins to do the work for them.

In the new study, the researchers mapped evolutionary relationships between the protein endowments of hundreds of organisms and used the information to build a new universal tree of life that included viruses. The resulting tree had four clearly differentiated branches, each representing a distinct "supergroup." The giant viruses formed the fourth branch of the tree, distinct from bacteria, archaea and eukarya (plants, animals and all other organisms with nucleated cells).

"The protein structures that other organisms share with viruses have a particular quality, they are (more widely) distributed than other structures," he said. "Each and every one of these structures is an incredible discovery in evolution. And viruses are distributing this novelty," he said.